South Korean soldiers have fired warning shots at a suspected North Korean drone that was spotted flying over the border separating the two countries.

A statement by South Korea's Joint Chiefs of Staff says the object was spotted flying above an observation post Wednesday along the western part of the border. The object turned around and returned to the North Korean side after it was fired upon.

The event signifies the increased tensions on the Korean peninsula days after North Korea carried out its latest nuclear test, which South Korean President Park Geun-hye described as an "an unacceptable challenge" to regional peace and security during a nationally televised address earlier Wednesday.

President Park called the United Nations Security Council to impose the harshest possible sanctions on Pyongyang over the test during her address. But she said unless China, North Korea's crucial diplomatic and economic ally, joins the effort, the isolated regime will carry out "a fifth or sixth nuclear test" and further destabilize the Korean peninsula.

"I believe the Chinese government will not allow the situation on the Korean peninsula to deteriorate further. The best partners are those that will hold your hand in difficult times," she said. "Holding the hands of someone in a difficult situation is the mark of the best partner.”

China angrily criticized North Korea over last week's nuclear test, but is seen as reluctant to impose extremely harsh sanctions against the North, fearing it would lead to the collapse of leader Kim Jong Un's government, leading to scores of refugees swarming over its shared border.

U.S. Secretary of State John Kerry is also urging China to take a tougher line against North Korea.

North Korea claims it detonated its first-ever hydrogen, or thermonuclear, bomb in last week's test, but its claims have been disputed by experts.

Park said South Korea will continue its loudspeaker broadcasts of anti-North propaganda statements at North Korean soldiers along the border separating the two countries, calling it an "effective psychological tool" against the regime.